Liquid crystal displays are displays that present a display using a liquid crystal composition. In a typical display mode, the amount of light transmitted is controlled by applying a voltage to a liquid crystal composition sealed between a pair of substrates to change the orientation of liquid crystal molecules in the liquid crystal composition depending on the voltage applied.
Generally, alignment films are formed on surfaces of the substrates to control the orientation of the liquid crystal molecules when no voltage is applied thereto. These alignment films are subjected to an alignment process for aligning the liquid crystal molecules in a predetermined direction.
Among known materials for alignment films are imide-containing polymers synthesized by dehydration and ring closure of a polyamic acid (see PTLs 1 and 2).
Whereas rubbing with a fibrous material has been commonly used as an alignment technique, photoalignment, which is a non-contact process, has increasingly been used as an alternative alignment technique in recent years.
In photoalignment, an alignment film is irradiated with light in a predetermined direction to impart predetermined alignment properties to the surface of the alignment film. As used herein, the term “light” is not limited to visible light, but encompasses ultraviolet radiation (ultraviolet light), i.e., electromagnetic radiation with shorter wavelengths than visible light.
Photoalignment involves the use of, for example, an alignment film material having a side chain containing a photoreactive group (see PTLs 3 to 5). The photoreactive group is, for example, a functional group isomerizable by exposure or a functional group crosslinkable by exposure.
PTLs 3 and 4 disclose that the use of an alignment film containing a polyvinyl compound having a particular chemical structure and a polyimide allows the pretilt angle to be stably maintained. The raw material for the polyvinyl compound is a polyfunctional monomer such as biphenyl dimethacrylate.